Capillary electrophoresis (CE) has been performed on polymer-stabilized bundles and sodium dodecyl sulfate (SDS) suspensions of high-pressure carbon monoxide (HiPco)-produced single-walled carbon nanotubes. Real-time Raman spectroscopy has been used for detection and characterization of the separation process. Radial-breathing-mode vibrational frequencies are sensitive to nanotube diameter. Monitoring of these modes demonstrates the separation of poly(vinylpyrrolidone) (PVP)-stabilized tubes into fractions of differing bundle composition. Separations on SDS suspensions indicate that CE is capable of separating bundled nanotubes from isolated individuals on the basis of differences in nanotube mobility, depending on changes in diameter or bundle size.